The GameSpy service, that is necessary to use the in-game server viewer in all game versions has stopped working for this game because of contract issues. There are alternative ways to query and join servers.

Solution 1
DeXuS an SWAT 4 Veteran released a tool years ago for a server browser to auto join servers updated his tool to accommodate for using the tool without having GameSpy support. Just click the link above.

Solution 2
MarkieBoy the creator of MarkMods released his own GameSpy replacement. (Fixes in-game server viewer) Just click the link above.

SWAT 4 is a tactical first-person shooter computer game developed by Irrational Games and released by Vivendi Universal on April 5, 2005. It is powered by Unreal Engine 2.0 technology enhanced by Irrational Games. An expansion to SWAT 4, entitled SWAT 4: The Stetchkov Syndicate, was released on February 28, 2006. In multiplayer, the player can choose among several modes:

COOP: Players complete SP missions in cooperation.

Barricaded Suspects: The usual team deathmatch mode.

VIP Escort: SWAT must escort the VIP to the extraction point while the suspects try to stop him.

Rapid Deployment: SWAT has to disarm bombs randomly placed throughout the map while the suspects try to stop them.

Smash & Grab (TSS only): A variation of 'capture the flag' – suspects try to transfer a briefcase to the exctraction point while SWAT must stop them.